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A B SUM C OUT 0 0 0 0 0 1 1 0 1 0 1 0 1 1 0 1 Assume we wish to add two 1 bit binary numbers and get a 2-bit result. A,B = 1-Bit Operands Result = C OUT , Sum B B B B B B B B B B B B B B B B Rather than numerical variables think of these as logical variables and build a half-adder . B B B B B B B B B =>Binary Number Adders
B Sum A 0 1 0 0 1 1 1 0 B A SUM = B A + A B SUM B A = B C OUT A 0 1 0 0 0 1 0 1 AB C OUT = OUT C A B SUM C OUT 0 0 0 0 0 1 1 0 1 0 1 0 1 1 0 1 Adders

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Defn: Gate Delay - The time it takes for a change of gate input to produce a change in gate output. Defn: Propagation Delay of Signal Path - The time it takes for a change of path input to produce a change in path output. Defn: Propagation Delay (between two points)-Longest path (measured in gate delays) between input and output Adders
A B SUM B A = OUT C What is the propagation delay from each input to each output for our circuit? From A/B to SUM 3 Gate Delays From A/B to COUT 1 Gate Delay Recall the XOR is built as: A B B A Adders

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A B SUM B A = OUT C
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